1. Field of the Invention
This invention relates to a toy model radio controlled, electric motor propelled flying wing.
2. Description of the Related Art
The flying wing is an aerodynamically efficient aircraft, in part because the entire body provides lift, while the fuselage section of a conventional aircraft introduces parasitic drag and offers little to no lift. Northrup describes basic flying wing theory in U.S. Pat. No. 2,406,506.
Commercially-available radio controlled, electric-motor-propelled toy flying wings have been derived from unpowered flying wings (gliders), typically used for soaring over slopes. The wings of such gliders are typically constructed using resilient EPP (expanded polypropylene) foam, offering light weight and impact resistance. To increase airframe stiffness, one or more spar shafts are embedded inside the EPP wings. The physical arrangement of the spar shaft(s) depends upon the design but could consist of a single shaft extending the major width of the wingspan or as an arrangement of shafts that effectively formed a pattern in the shape of the letter “A”.
Flight control of a toy flying wing is generally made possible through the use of two control surfaces (elevons) on the trailing edge of each wing. Servos are coupled to each elevon to actuate the elevon, thereby providing control of the aircraft in flight. Vertical stabilizers (winglets) are typically used at the wingtips for directional stability and to reduce induced drag due to wingtip vortices.
Typically no landing gear is used because these toy craft are hand launchable and can land gently in the grass or can be hand caught.
Slope soaring involves the use of rising wind available at hilly terrain as the principal energy source for climbing. Frequently, such hilly terrain is unavailable or inconveniently located, or the weather conditions are not conducive to slope soaring. Because of this, an electric propulsion system has been added.
An electric motor is secured to the flying wing glider on the center wing chord line, positioned flush with the trailing edge of the wing, with the motor shaft projecting rearward beyond the trailing edge. The motor shaft accepts a pusher thrust configuration propeller. Commonly, but not exclusively used, is an inexpensive electric motor known in the trade as the “Speed 400”.
Because the motor is attached directly on top of the wing surface, and the trailing wing edges are swept back, it is necessary to trim the wing trailing edges somewhat in order to provide clear space for the propeller to spin. In operation, the propeller operates very closely to the trimmed trailing edge. This causes propeller thrust inefficiencies because the wing, and in particular, the trailing edge of the wing generates turbulence that interferes with smooth propeller air flow. This configuration also increases the audible noise level generated by the propeller system.
With the introduction of an electric-motor-powered thrust system came the requirement for a larger on-board battery containing sufficient energy to drive the electric motor at a rated speed for a reasonable amount of time. Because the airfoil thickness of original flying wing glider designs does not fully accommodate the larger battery inside the wing, the battery is typically placed on top of, underneath, or is partially embedded into the wing. The battery is typically constructed of multiple dry cells, electrically connected in series. Cell technologies include Nickel Cadmium (NiCD), Nickel Metal Hydride (NiMH), and Lithium ion.
Several commercially-available powered flying wing products use a relatively large thermoplastic fuselage that covers the battery and the motor on the top surface and is secured with small strips of adhesive-backed hook-and-loop tape (generally known as Velcro). Velcro is also the principal means of securing the battery. The disadvantages of this design include substantial interference from the fuselage with airflow to the rearwardly-located pusher propeller. Upon hard nose impact with the earth or a stationary object, the thermoplastic cracks or shatters and the battery, also secured to the plane using Velcro fasteners, can eject from the craft, posing a human safety hazard and potentially damaging the battery and all electronics connected to the battery.